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Lesions of the internal segment of the globus pallidus are increasingly being utilized in the surgical treatment of advanced Parkinson's disease, yet studies to demonstrate the safety and efficacy of these procedures are only now being completed. The importance of procedural variations between centres in the outcome of pallidotomy is not yet known. In order to compare accurately results between centres, carefully designed, prospective studies are needed. The authors utilized blinded, randomly evaluated videotaped examinations of pre- and post-operative patients undergoing microelectrode-guided GPi pallidotomy. Their results demonstrate significant effects on contralateral akinesia and tremor in the "off" state, and striking attenuation of levodopa-induced dyskinesias in the "on" state. More modest effects on postural stability and gait disturbance were seen only in non-blinded evaluations. This type of study design should enable many of the outstanding issues related to pallidotomy indications, procedures and outcomes to be addressed.

In an attempt to refine the indications for posteroventral pallidotomy (PVP) the authors instituted strict selection criteria which are based on the experience gained from the first 60 pallidotomy patients treated at their institution. In addition to clinical evaluation, all pallidotomy candidates undergo neuropsychological testing and 18F-fluoro-deoxyglucose utilization positron emission tomography (FDG/PET). The data from which these criteria were developed are presented as are early clinical results. The authors demonstrate that these criteria enhance the efficacy of the procedure by assuring therapeutic response and reducing the incidence of post-operative dementia. Their indications and contraindications for pallidotomy are discussed.

Posteroventral pallidotomy (PVP) has gained a worldwide acceptance after its reintroduction by Laitinen et al. in 1992 (56) and many studies have since been published. A review of the recent literature reveals that there is variation in the clinical indications for this procedure, the surgical technique used and the assessment of results. There is no uniform practice in the choice of the anatomical target point within the globus pallidus, the imaging of the target structure, the intraoperative assessment of the physiological target and the mode of evaluation of the surgical results. Although some neurosurgeons advocate that the lesion should be in the lateral pallidum, the majority insist it should be in the medial pallidum. It is shown here that, as long as the lesion is made at the posterior and ventral parts of the globus pallidus, it will necessarily include aspects of both medial and lateral posteroventral pallidum. There is a common agreement on the effectiveness of pallidal surgery on the L-dopa induced dyskinesias, but, its long-term effects on tremor, akinesia, freezing of the gait and other genuine parkinsonian symptoms need more extensive evaluation. The assessment of the outcome of pallidal surgery in terms of the patient's disability, quality of life and coping abilities following surgery seems to have been neglected.